1. Field of the Invention
The present invention broadly relates to multiplex keyway systems for keyed mechanical locks and, more particularly, to systems and methods for creating extended families of keyways and associated keys which share a common master key for operating any lock having one of the keyways.
2. Description of the Related Art
Mechanical locks are currently the most common mechanisms providing access control for doors and other limited-availability spaces or locations, and are in widespread use to guard the entrances to the vast majority of personal residences, commercial offices, factories and manufacturing plants, educational institutions, hotel rooms and a host of other sites, as well as to protect or secure readily movable or transportable articles such as bicycles, land, sea and air vehicles, tool and other article holders, and numerous other objects from use or removal or theft by unauthorized or unintended individuals. One of the most popular lock designs in extensive practical use is the so-called pin tumbler lock, parts of which are variously shown by way of example in FIGS. 1 and 3. The lock typically comprises a rotatable cylinder tube 102, called the plug, which is linked to the underlying locking mechanism. Disposed about the circumference of the plug is a shell (not shown), which in a fixed-use application is normally nonremovably secured to a door or housing. Relative rotation of plug 102 within the shell in response to a torque generated by user-manipulation of a key 104 (FIG. 2) that is inserted within the keyway of plug 102 (see FIG. 3) operates the locking mechanism. In the locked or nonoperating state of the lock such rotation of plug 102 is prevented by a set of longitudinally displaceable, spring-loaded pin stacks 106 that protrude from a series of bores defined in the top of plug 102 (FIG. 1) and extend into corresponding bores defined in the shell, with a compression spring 108 disposed within each shell bore urging each respective pin stack toward the axis of plug 102. Each pin stack 106, which is typically formed of multiple predetermined lengths of pins, thereby defines one or more pin stack discontinuities or cuts or breaks or separations 110 between the individual pins, along and generally perpendicular to the length of that stack. Completing the lock is a tail piece (not shown) connected to the plug and configured to transmit a torque, resulting from relative rotation of plug 102 within the shell, in either the unlocking (i.e. opening) or locking direction.
With no key in the lock (FIG. 1), the respective compression spring 108 presses each pin stack 106 into its rest position within the plug and shell, with each of the pin stack separations or discontinuities 110 disposed within the plug. When, however, a cut or bitted key 104 is inserted into the plug, as shown in FIG. 3, through a lock keyway having a profile complimentary to that of the key, the pin stacks 106 are variously raised within the plug and shell by the respective key bittings. If the key has been cut to open that particular lock—i.e. the key bittings correspond to the pin stack separation heights or locations—then the fully-inserted key 104 will lift each pin stack so that one of its discontinuities is aligned at a border 112, called the shear line, which is located between the plug and the circumferential shell. The plug 102 can then freely rotate—in response to a turning torque applied to the key by a user—relative to the shell to thereby unlock or relock the door or other location or article. On the other hand, the plug 102 will be prevented from rotating relative to the shell if any single pin stack either is insufficiently lifted by the corresponding key bitting so that the pin stack separation 110 remains below the shear line (i.e. within the plug) or is lifted too far by the corresponding key bitting so that the pin stack separation is advanced above the shear line 112 (i.e. into the shell). The series of cut depths of a key 104 under the plural respective pin stack positions—i.e. the bitting of the key—defines the combination or code necessary to operate a particular lock; a key that is bitted to the wrong depth in even a single pin stack position will not operate that lock. Typical residential and commercial locks generally have five or six pin stacks 106, or much less commonly four or seven stacks, with from four to ten distinct cut depths generally used on each.
The available number of combinations based on the topology of any specific key are seemingly limited only by attainable manufacturing tolerances. In practice, however, there are a number of limiting factors. The angle between adjacent key cuts must be controlled to assure the smooth insertion into and extraction of the key from a lock keyway. Keys with very deep cuts are, moreover, prone to breakage, deformation, etc. and are therefore generally avoided Perhaps the most serious limitation to the number of available combinations is that caused by master keying, i.e. creating an arrangement or grouping of families having two or more levels of keying. Master keying is commonly implemented by providing multiple sepaations or discontinuities in a pin stack; one separation is used for operating the lock in response to a change or low level key—i.e. a key specially bitted to operate for example only that lock—and the other for a master or top level key that is bitted to operate all or a predetermined plurality of differently-configured locks, for example in multiple families of a hierarchical multiplex grouping of keyways.
There is for a number of reasons a common need to increase or extend the number of distinct keys, each for operating a corresponding different lock cylinder, that can be used on the same project, such for example as a hotel, school, manufacturing facility or office complex. A single keyway profile, and the maximum plurality of differently-bitted keys having a complementary profile that can be utilized in a master keyed arrangement, may be insufficient to fully populate all of the doorways or other entry or access openings needed in a single facility or location. One way in which to extend the number of available distinct key combinations is through the use of multiplex keyways which are constructed in hierarchies with a top-level keyway and low-level keyways all configured with blocking elements that prevent the incorrect keys from entering unintended keyways. The principle of operation of such a multiplex keyway system is the blocking of one low-level key profile or section from entering a different low-level keyway, while allowing a master key to both enter and unlock all of the low-level locks.
The simplest prior art multiplex hierarchy is illustrated in FIG. 4; low-level keyways 10 and 20 are configured to accommodate the entry of keys 101 . . . 10n and 201 . . . 20n, respectively. All keys 20n are blocked from entering keyway 10, and all keys 10n are blocked from and therefore unable to enter keyway 20. This arrangement allows the same key combinations (i.e. bitting combinations) to be reused for keys to access each of the low-level keyways 10, 20 without unwanted key interchange. If the locks are master keyed, then a master key 12 is configured so that it can enter both the low-level keyway 10 and the low-level keyway 20 and operate all of the locks of both.
If it is then desired to increase the number of available combinations of keys, a new keyblank is produced with a profile that is defined by modifying the profile of the master key 12 to, for example, increase the size of one or more surface features of the master key profile. The new system thus has a new keyway 20′—with a profile complementary to the new keyblank—which will accept the new keys 20′1 . . . 20′n but which blocks entry of the old keys 10n and 20n. The old keyways 10 and 20 correspondingly block the new keys 20′1 . . . 20′n. And all of the keyways 10, 20 and 20′ will accept the master key 12. Moreover, the extended multiplex hierarchy now has fifty percent more key combinations available than the original multiplex hierarchy that included only the keyways 10 and 20.
In practice, lock makers often create multiplex families of more, often many more, than two base-level key sections; indeed, some families have 80 or more sections. However, at some point any multiplex hierarchy reaches a practical limit of the number of families that can be added to further extend the number of available unique lock-and key combinations within the hierarchy using currently-practiced procedures, and there accordingly remains an unsatisfied need for ways to further extend such hierarchies to additional key-keyway combinations.
Another technique currently used for increasing the number of available key combinations involves extending a simplex keyway into a family of multiplex keyways. In a simplex keyway system, only a single independent key can enter the keyway and operate a lock configured with the proper bitting combination. In this technique, a blank for the key configured to operate the existing or “old” simplex keyway is double milled to produce a master key capable of entering the new keyway(s) and operating the associated locks. This, however, often leads to “weak” master keys, and the double milled key may or may not fit into both the old and new keyways at the same position, rendering lock operation with the key unreliable.
A need therefore exists for a positional multiplex keyway system and method that can extend a simplex keyway into multiplex families, and extend ordinary multiplex families into larger multiplex families.